VCSEL Array LIDAR Transmitter with Small Angular Divergence

ABSTRACT

A light detection and ranging (LIDAR) transmitter includes a plurality of light emitters that generate a plurality of optical beams. A first lens is positioned in an optical path of the plurality of optical beams at a distance from at least one of the plurality of light emitters that is less than a focal length of the first lens. The first lens converges the plurality of optical beams to a converged optical beam having a beam waist. A second lens is positioned in the optical path of the converged optical beam. The second lens projects the converged optical beam to a target range. The position of the second lens and an emission width of at least one of the plurality of light emitters are configured to provide a desired field-of-view of the LIDAR transmitter at the target range.

RELATED APPLICATION SECTION

The present application is a non-provisional of copending U.S.Provisional Patent Application Ser. No. 62/538,149, filed Jul. 28, 2017,and entitled “VCSEL Array LIDAR Transmitter with Small AngularDivergence.” The entire content of U.S. Patent Application Ser. No.62/538,149 is incorporated herein by reference.

The section headings used herein are for organizational purposes onlyand should not to be construed as limiting the subject matter describedin the present application in any way.

INTRODUCTION

Autonomous, self-driving, and semi-autonomous automobiles use acombination of different sensors and technologies such as radar,image-recognition cameras, and sonar for detection and location ofsurrounding objects. These sensors enable a host of improvements indriver safety including collision warning, automatic-emergency braking,lane-departure warning, lane-keeping assistance, adaptive cruisecontrol, and piloted driving. Among these sensor technologies, lightdetection and ranging (LIDAR) systems take a critical role, enablingreal-time, high resolution 3D mapping of the surrounding environment.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teaching, in accordance with preferred and exemplaryembodiments, together with further advantages thereof, is moreparticularly described in the following detailed description, taken inconjunction with the accompanying drawings. The skilled person in theart will understand that the drawings, described below, are forillustration purposes only. The drawings are not necessarily to scale,emphasis instead generally being placed upon illustrating principles ofthe teaching. The drawings are not intended to limit the scope of theApplicant's teaching in any way.

FIG. 1 illustrates the operation of a LIDAR system according to thepresent teaching.

FIG. 2 illustrates an embodiment of a LIDAR system using two lasersaccording to the present teaching.

FIG. 3 illustrates an embodiment of a multi-emitter laser source for aLIDAR transmitter according to the present teaching.

FIG. 4 illustrates a diagram of the cross-section of an embodiment of anilluminator for a LIDAR transmitter of the present teaching.

FIG. 5A illustrates a measurement point cloud for an embodiment of asingle-wavelength 2D multi-emitter LIDAR transmitter of the presentteaching.

FIG. 5B illustrates a measurement point cloud for an embodiment of atwo-wavelength 2D multi-emitter LIDAR transmitter according to thepresent teaching.

FIG. 6 illustrates a perspective view of a schematic diagram of thestructure of a prior art bottom-emitting VCSEL laser used in someembodiments the LIDAR transmitter of the present teaching.

FIG. 7 illustrates a schematic diagram of an embodiment of a 2Dmonolithic VCSEL array with twenty-five separate laser emittersaccording to the present teaching.

FIG. 8 illustrates a schematic diagram of an embodiment of a 2Dmonolithic VCSEL array with twenty-five separate laser emitterscomprising sub-apertures according to the present teaching.

FIG. 9 illustrates a schematic diagram illustrating light projected by asingle emitter in a single lens LIDAR transmitter system according tothe present teaching.

FIG. 10 illustrates a schematic diagram of light projected by multipleemitters in a single lens LIDAR transmitter system according to thepresent teaching.

FIG. 11A illustrates a schematic diagram showing an expanded view oflight projected by multiple emitters in a single lens LIDAR system withhigh angular divergence emitters.

FIG. 11B illustrates a schematic diagram illustrating a condensed-viewof light projected by the system of FIG. 11A that shows the far field.

FIG. 12 illustrates a schematic diagram of an embodiment of a two-lensilluminator that projects light in a small angular divergence LIDARtransmitter according to the present teaching.

FIG. 13 illustrates a schematic diagram of an embodiment of amultiple-transmitter-array small angular divergence LIDAR transmitteraccording to the present teaching.

FIG. 14A illustrates a schematic diagram of an expanded view of a smallangular divergence LIDAR transmitter illuminator utilizing multipletransmitter arrays on a single substrate according to the presentteaching.

FIG. 14B illustrates a schematic diagram of a condensed-view of thesmall angular divergence LIDAR transmitter of FIG. 14A.

FIG. 15 illustrates schematic diagrams of scaled condensed views ofembodiments of the small angular divergence LIDAR transmitters of thepresent teaching that indicate relative independence of the separationbetween transmitter arrays.

FIG. 16 illustrates an embodiment of an illuminator for amulti-wavelength LIDAR system using multiple transmitter arraysaccording to the present teaching.

FIG. 17 illustrates a measurement point cloud that can be generated withthe illuminator described in connection with FIG. 16.

DESCRIPTION OF VARIOUS EMBODIMENTS

The present teaching will now be described in more detail with referenceto exemplary embodiments thereof as shown in the accompanying drawings.While the present teaching is described in conjunction with variousembodiments and examples, it is not intended that the present teachingbe limited to such embodiments. On the contrary, the present teachingencompasses various alternatives, modifications and equivalents, as willbe appreciated by those of skill in the art. Those of ordinary skill inthe art having access to the teaching herein will recognize additionalimplementations, modifications, and embodiments, as well as other fieldsof use, which are within the scope of the present disclosure asdescribed herein.

Reference in the specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the teaching. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment.

It should be understood that the individual steps of the methods of thepresent teaching can be performed in any order and/or simultaneously aslong as the teaching remains operable. Furthermore, it should beunderstood that the apparatus and methods of the present teaching caninclude any number or all of the described embodiments as long as theteaching remains operable.

The present teaching relates to Light Detection and Ranging Systems(LIDAR) that measure distances to various objects or targets thatreflect and/or scatter light. It is desirable that LIDAR systems have asmall footprint, high measurement resolution, and high detectionsensitivity. VCSEL-array-based transmitters offer the promise ofproviding these benefits. Improvements are needed in the optical designof these VCSEL-array-based LIDAR transmitters in order to increaseperformance and to reduce size, weight, power, cost and complexity ofLIDAR systems. As one example, LIDAR transmitter designs are needed thatproduce a small angular divergence in a compact package.

FIG. 1 illustrates the operation of a LIDAR system 100 according to thepresent teaching that is implemented in a vehicle. The LIDAR system 100includes a laser projector, also referred to as an illuminator, thatprojects light beams 102 generated by a light source toward a targetscene and a receiver that receives the light 104 that reflects off anobject, shown as a person 106, in that target scene. LIDAR systemstypically also include a controller that computes the distanceinformation about the object 106 from the reflected light, and anelement that can scan or provide a particular pattern of the light thatmay be a static pattern across a desired range and field-of-view (FOV).The receiver and controller are used to convert the received signallight into measurements that represent a pointwise 3D map of thesurrounding environment that falls within the LIDAR system range andFOV. In various embodiments, the controller can be a simple electricalcircuit or can be a more complicated processor, depending on theparticular application.

The laser source and optical beam projection means that form theilluminator and the receiver may be located on the front side of avehicle 108. A person 106, and/or another object, such as a car or lightpole, will provide light reflected from the source back to the receiver,and a range, or distance, to that object is determined. As is known inthe art, a LIDAR receiver calculates range information based ontime-of-flight measurements of light pulses emitted from the lightsource. In addition, known information about the optical beam profilethat illuminates the scene in a target plane associated with aparticular range and based on the particular design of the source andprojector system is used to determine location information about thereflecting surface, thereby generating a complete x, y, z, orthree-dimensional picture of the scene. In other words, the pointwise 3Dmap of the surrounding environment represents a collection ofmeasurement data that indicates position information from all thesurfaces that reflect the illumination from the source to the receiverwithin the field-of-view of the LIDAR system. In this way, a 3Drepresentation of objects in the field-of-view of the LIDAR system isobtained. The pointwise 3D data map may also be referred to as ameasurement point cloud.

One feature of the present teaching is that the illuminator may includelasers that emit optical beams with individual, distinct wavelengths.Typically, LIDAR systems do not utilize different laser wavelengths toenable improvements in the angular resolution of the LIDAR system. Inparticular, one feature of LIDAR systems of some embodiments of thepresent teaching is that they use multiple laser wavelengths to enablefiner angular resolution and performance in a low-cost, compact opticaldesign. Furthermore, multi-wavelength LIDAR systems of the presentteaching can provide a simple path to improved security andparallelization. See, for example, U.S. patent application Ser. No.15/456,789, entitled “Multi-Wavelength LIDAR System” filed on Mar. 3,2017 and U.S. Patent Application Ser. No. 62/396,295, entitled “WDMLidar System” filed on Sep. 19, 2016. U.S. patent application Ser. Nos.15/456,789 and 62/396,295 are both assigned to the present assignee andare herein incorporated by reference.

FIG. 2 illustrates an embodiment of a multi-wavelength LIDAR system 200using two lasers according to the present teaching. The first laser 202operates at a first wavelength, and the second laser 204 operates at asecond wavelength. The lasers may include integrated or separatecollimation optics that form part of an optical projection element thatis used to form a beam profile at various target planes across the FOVand range of the LIDAR system. The illuminator 206 can also include anoptical device 208 that further shapes and projects the optical beams toform particular beam profiles at target plane 210. In variousembodiments, different types of optical devices can be used to form theoptical projection element including, for example, one or more oflenses, diffractive optics, prisms, thin-film wavelength sensitivedevices, and partially reflecting mirrors. Single lens or multi-lensoptical elements may be used.

A receiver 212 receives light reflected off the surface of objects atvarious target planes 210 in the FOV and range of the LIDAR system. Ifdifferent wavelengths are used, the receiver 212 may be able todistinguish light from the two wavelengths emitted by the sources 202,204. In this case, reflected illumination from each wavelength isprocessed separately. A controller 214 is used to process the receivedlight. The controller 214 provides LIDAR data at an output 216. Thecomplexity of the controller 214 depends on the particular configurationof the LIDAR system. The controller 214 may be used to control the lasersources 202, 204. In various embodiments, the controller 214 maycomprise various electrical circuits, integrated circuits,microprocessors, or computers. It is relatively straightforward to add Nlasers with the same or different wavelengths to the LIDAR system shownin FIG. 2. In some embodiments, there are additional optical elementsthat collimate the light and provide the desired FOV.

A projection element as described herein is an element that collimatesor otherwise shapes and/or projects a laser beam or multiple laser beamsin a particular direction. A projection element can comprise one or moreoptical devices positioned in the path of the optical beams. Thesedevices and their positions, together with the initial shape and pathsof the beam or beams emitted from the laser source, produce the desiredbeam profile, which is a combination of beam shape and/or beam positionat a particular point in space. Upon receipt of light reflected offobjects at a receiver of the LIDAR system, the system generates ameasurement point cloud, or pointwise data map, that is based on thepattern of light projected by the illuminator, and its performanceparameters including angular resolution and field-of-view.

One feature of the present teaching is the ability to use differentwavelengths to produce different LIDAR FOV, range, and/or resolution ina compact system. The light beams at the two or more wavelengths may beable to share at least some of the same optical devices that form theprojection element, and yet still realize different beam profiles thatresult in a measurement point cloud that represents different rangeand/or FOV and/or resolution at each wavelength. For example, oneproblem with prior art LIDAR systems that use a signal wavelength isthat the launch power required to reach 100-meter range is so high thatfor close proximity reflections (e.g. a few meters) the receiversaturates. Consequently, these prior art LIDAR systems are blind to nearobjects. This problem can be solved with a two-wavelength system, wherethe first wavelength is used for a 100-meter range, but the secondwavelength has a low power only meant for near-proximity measurements.Multi-wavelength measurements can be performed simultaneous using acontroller with parallel computing capability. The extension of thisconfiguration to more than two wavelengths is relativelystraightforward.

Another feature of the present teaching is that lasers with additionalwavelengths can be added to perform functions other than LIDAR ranging.For example, additional lasers can be added to provide measurements ofthe orientation of optical devices within the LIDAR system. The lightfrom these sources at additional wavelength may serve a sole purpose toprovide angular measurement of the elements that project the opticalbeams and/or replicate or scan the optical beams. In some embodiments,MEMS devices are used to project beams, and it can be important to havedirect feedback of the mirror position. Another laser combined with anappropriate receiver measurement system could provide direct anglemeasurement of mirror position. A natural extension of the aboveembodiments would be to use a plurality of lasers of the same wavelengthin each case, that is, either a 1D or 2D array of lasers of eachwavelength instead of a single laser of each wavelength.

In some systems, a single large lens is used to both collimate as wellas set the projection angle of each VCSEL device. It should be notedthat instead of a single lens, two or more lenses could be used as partof the shared lens configuration. One aspect of using a shared optic forboth collimation and projection angle is that there is a direct mappingbetween the lateral position of the VCSEL device relative to the centralaxis of the lens and the pointing angle of the projected laser beam. Thelateral distance between two VCSEL lasers of the same, or similar,wavelength will correspond to the difference in projection anglescreated by the shared lens system.

Furthermore, since the VCSEL device is not an ideal point source, butinstead has a finite lateral size, there will be an additionaldivergence that cannot be reduced by the optics without also shrinkingthe FOV of the overall optic system. Also, the shared-optic approachusing lasers with the same or similar wavelength may lead to beamoverlap or gaps in the 3D measurement span depending on the finite sizeof the VCSEL, the divergence of the collimated beams, the number ofVCSEL devices, and the FOV, among other parameters.

One feature of LIDAR systems of present teaching is the use of VCSELchips with clusters of emitting apertures to take advantage of thehigher optical power and large diameter cluster provided by thesedevices. As described herein, a VCSEL device is not an ideal pointsource, but rather has a finite lateral dimension. Furthermore,high-power top-emitting VCSEL lasers used for LIDAR illuminationtypically use multiple light emitting sub-apertures to reach therequired high-power output. These multiple sub-apertures form a clusteror group, and ideally are located as close as physically possible, whilestill maintaining the required electro-optic efficiency.

In some embodiments, the VCSEL array is a two-dimensional array. In someembodiments, the VCSEL array is monolithic and the lasers all share acommon substrate. A variety of common substrate types can be used. Forexample, the common substrate may be a semiconductor material. Thecommon substrate may also include a ceramic material.

In some embodiments, the VCSELs are top-emitting VCSELS. In otherembodiments, the VCSELs are bottom-emitting VCSELS. The individualVCSELs may have either a single large emission aperture, or theindividual VCSELs may be formed from two or more sub-apertures within alarger effective emission diameter. A group of sub-apertures forming alarger effective emission region is sometimes referred to as a cluster.

FIG. 3 illustrates a multi-element emitter laser source 300 with twodifferent VCSEL wavelengths interleaved uniformly in the verticaldirection. The embodiment shown in FIG. 3 illustrates a single commonsubstrate 304, but it will be clear to those skilled in the art thatmultiple substrates could also be used. There are six VCSEL bars 306,308. The cluster VCSEL devices 302 of the bars 306 emit at one commonwavelength. These are the bars 306 labeled “VCSEL λ1” in the figure. Thecluster VCSEL devices 302 of the dark bars 308 emit at a differentwavelength. The bars 308 are labeled “VCSEL λ2” in the figure. A totalof thirty cluster VCSEL devices 302 are shown.

The illuminator used in connection with the multi-element emitter lasersource 300 of FIG. 3 can use a shared lens system for both collimationand projection of the beams over the desired FOV. FIG. 4 illustrates adiagram of a cross-section of an embodiment of an illuminator 400 for amulti-wavelength LIDAR system of the present teaching that uses amulti-wavelength laser source shown in FIG. 3. The illuminator 400includes the multi-emitter laser source 402, and a projection element404 comprising a wavelength multiplexer 406 and a first lens 408. Theprojection element 404 is used to project the laser beams 410, 412emitted from the laser source 402. The emitters for the multi-emitterlaser source 402 are located on a VCSEL substrate 414.

The projection element 404 in FIG. 4 comprises two optical devices 406,408. The first optical device is a wavelength multiplexer 406 that is awavelength sensitive optic that acts to combine the laser beam 410 atone of the two wavelengths and from one optical path with the laser beam412 at the other of the two wavelengths that is on another optical pathonto a common optical path. In some embodiments, wavelength multiplexerscomprise a diffractive optic that is configured to substantially shiftthe optical path of one wavelength while letting the second wavelengthpass through undisturbed. Diffractive optic elements are well known inthe art and can be used to provide precise beam steering and beamshaping of lasers. In some embodiments, a wavelength-sensitivediffractive optical element is used. In other embodiments, an array ofrefractive optics, such as prisms, is used. The second device is a lens408 that is used to further project and shape the laser beams 410, 412to form a desired pattern of beam shapes and beam positions at thetarget plane of the LIDAR system.

FIG. 4 illustrates how the light from two VCSEL bars of differentwavelength travels through the optical system. For clarity, only thelaser beams 410, 412 from two VCSEL emitters are shown ray traced. FIG.4 illustrates only a single lens 408, however, it will be clear to thosewith skill in the art how to implement a two-lens, or multi-lens systemas described, for example, in connection with FIG. 12 below with themulti-wavelength system illustrated in FIG. 4.

In operation, light from the beam profiles formed at a target plane bythe illuminator is reflected from the surface of objects in that targetplane. A target plane in a LIDAR system is a virtual reference pointthat operates over a complete range and field-of-view. There are manydifferent target planes at various distances from the LIDAR module suchthat the system can generate three-dimensional representation of theobjects in the field-of-view and range being probed by the LIDAR system.A portion of the light reflected off the surfaces of objects illuminatedby the optical beam profiles in the target plane is directed toreceivers. The receivers detect the light and then convert the receivedoptical signal to an electrical signal. A controller electricallyconnected to the light sources and to the receiver converts the receivedsignal into a measurement point cloud. The angular resolution of pointsin the measurement point cloud depends of the relative position of thebeam profiles at a target plane, as described further below. It will beclear to those skilled in the art that many other variations of theembodiment of the illuminator 400 illustrated in FIG. 4 are within thescope of the present teaching. For example, VCSEL lasers may be locatedin a common surface, either planar or curved. It will also be clear tothose skilled in the art that some deviation of the VCSEL away from acentral surface, curved or flat, can be tolerated.

FIG. 5A illustrates a measurement point cloud 500 for an embodiment of asingle-wavelength 2D laser source illumination according to the presentteaching. The distance between the vertical spacing 502 of themeasurement points 504 determines the vertical angular resolution. Thehorizontal spacing 506 of the points on the point cloud determines thehorizontal angular resolution of the point cloud.

FIG. 5B illustrates a measurement point cloud 550 for an embodiment of atwo-wavelength 2D laser source illumination of the present teaching. Ameasurement point corresponding to a VCSEL with λ1 is shown as a circle552, a measurement point with a VCSEL with λ2 is shown as a triangle554. A composite point cloud includes a point cloud derived fromreflections received at λ1 and a point cloud derived from reflectionsreceived at λ2.

For example, the measurement point cloud 550 illustrated in FIG. 5B canbe realized using the multi-emitter laser source with the pattern ofVCSEL emitters of different wavelengths illustrated in FIG. 3 togetherwith the illuminator configuration of FIG. 4. A portion of the lightfrom optical beams generated by the illuminator at the target plane isreflected by the surface of an object and incident on one or moreoptical receivers that are capable of detecting light at particularwavelengths. The resulting measurement point cloud 550 includes pointsrepresenting light from the different beam profiles that are atdifferent wavelengths.

Referring to FIGS. 3-5, different wavelength VCSEL bars 306, 308 occupydifferent rows of the laser source in the vertical direction, andindividual VCSEL devices 302 in different rows have their centers offsetin the horizontal direction. The optical beams from emitters indifferent wavelength bars are projected by the projection element 404 sothat the optical beam positions are slightly offset at the target planein the vertical direction. This causes the offset 556 in the measurementpoint cloud. The offset in the center position of the VCSELs in adjacentbars, together with the design of the projection element causes themeasurement points representing each wavelength to be interleavedhorizontally along the offset vertical lines. The angular resolution ofthe measurements in a given dimension is directly related to the offsetof the points in that dimension, which is related directly to thepositions of the optical beams in that dimension at the target plane.

Referring to both FIG. 5A-B, a performance tradeoff associated withusing a two-wavelength solution is clear. In the embodiment shown inFIG. 5, the optical beams at one wavelength travel substantiallyuninterrupted, but the optical beams at the second wavelength areintentionally shifted in position to substantially overlap in onedirection with the optical beams at the first wavelength. The offset 556in position of the optical beams at each wavelength indicated in thedrawing in FIG. 5B can be adjusted based on the design of the wavelengthmultiplexer. For example, in some embodiments, the wavelengthmultiplexer 406 in FIG. 4 is specifically designed to provide aparticular offset 556 in position of the optical beams at eachwavelength. In various embodiments, various devices in the projectionelement are used to position the beams of the lasers at the twowavelengths. These same devices, or other devices, may alter the beamshapes as well their positions at the target plane.

As compared to the single wavelength embodiment of FIG. 5A, theembodiment described in connection with FIG. 5B doubles the angularresolution in a preferred direction, which in this case is thehorizontal direction, at the expense of halving the angular resolutionin the perpendicular direction. This is accomplished while keeping theoverall physical size of the system relatively constant. In someapplications, finer resolution in one direction may be preferred ornecessary, for instance if instead of a pedestrian, the system needs todistinguish a pole or tree with a cross-section of only 100 mm. At 30 m,we would need an angular resolution that is less than 0.15 degrees. Forautomotive LIDAR systems, it could be highly desired to have a verysmall angular resolution in the horizontal direction, at the expense ofwider angular resolution in the vertical since common objects that needto be recognized, such as humans, poles, and trees are tall but narrow.In some embodiments, the angular resolution of the measurement pointcloud is less than 0.4 degree at a predetermined distance from thetarget plane to the optical projection element.

One feature of the present teaching is that single element emitters andmulti-element emitters light sources operating at different wavelengthsdo not need to be located on the same surface. Another feature of thepresent teaching is that the surfaces may be oriented along differentspatial planes in three-dimensional space. For example, the planes maybe on two orthogonal planes. In some embodiments, we use a plurality ofsurface emitting lasers made up of at least two groups of lasers withdifferent wavelengths. We also make use of three-dimensional space andeach group of lasers are oriented in two or more surfaces, planar orcurved, that are not necessarily orthogonal. In these embodiments, thepackaging and optical alignment complexity increases relative toembodiments in which the lasers are co-located on a common surface, butwe are able to increase the resolution angle across the fullfield-of-view in both orthogonal directions, without any compromise.This provides both higher precision as well as full access to all thecapabilities associated with more than one wavelength. That is, it ispossible to realize simultaneous operation, redundancy, security andother features of multi-wavelength operation.

One feature of the present teaching is that the small angular divergenceLIDAR transmitter of the present teaching provides a compact LIDARmodule especially suited to LIDARs that operate with a range requirementof about 100 meters. Another feature of the small angular divergenceLIDAR transmitter of the present teaching is that it may utilize asolid-state optical emitter. Consequently, the LIDAR transmitter of thepresent teaching can be built utilizing no moving parts. In addition,multiple lasers, which may emit at the same or different wavelengths,can be used to establish a one-to-one mapping between each laser and a3D measurement point cloud.

FIG. 6 illustrates a schematic diagram of a perspective view of astructure of a known bottom-emitting VCSEL laser 600 that can be used inthe small angular divergence LIDAR transmitter of the present teaching.Note that the emission area of the VCSEL laser 600 typically ranges froma few microns in diameter for mW power operation, up to 100 micronsdiameter or more for 100 mW and greater CW power operation. Variousembodiments of the present teaching use a variety of known VCSEL laserdevices, including top-emitting VCSELs, bottom-emitting VCSELS, andvarious types of high-power VCSELs. The VCSELs is fabricated on asubstrate 602 that can be GaAs, or other semiconductor material. Ann-type distributed Bragg reflector (DBR) 604 is positioned on thesubstrate. An active region 606 is constructed on the n-type DBR 604,followed by an aperture 608 that can be made from an oxide material. Ap-type Distributed Bragg Grating DBR 610 is then grown on the activeregion 606. Typically, the p-type DBR is highly reflecting, and then-type DBR is partially reflecting, resulting in light output 612 fromthe bottom, substrate-side of the layer structure. The active region606, oxide aperture 608 and p-type DBR 610 are formed in a mesastructure 614. A top contact 616 and a bottom contact 618 are used toprovide an electrical current to the active region 606 to generate theoutput light 612. An oxide aperture 608 provides current confinement tothe active region 606. The top contact 616 is p-type, and the bottomcontact 618 is n-type. Emission apertures 620 are formed in the bottomcontact 618 to allow the output light 612 to emerge from the bottom,substrate side of the bottom-emitting VCSEL 600. This type of VCSEL maybe a single element, or multiple VCSELS can be fabricated as one- ortwo-dimensional arrays on the substrate 602.

FIG. 7 illustrates a schematic diagram of an embodiment of a 2Dmonolithic VCSEL array 700 with twenty-five separate laser emitters 702of the present teaching. Each laser emitter 702 has an emission aperture704 of diameter, a. Emission from each single laser emitter 702substantially fills the full emission aperture 704. Each laser emitter702, therefore, generates a laser beam with diameter, a, equal to thediameter of the emission aperture 704. The laser emitters 702 are spaceduniformly in the horizontal direction with a spacing dx 706. The laseremitters 702 are spaced uniformly in the vertical direction with aspacing dy 708. The overall size of the array, measured from the centersof the outermost lasers is distance Dx 710 in the horizontal directionand distance Dy 712 in the vertical direction. The actual chip size willbe slightly larger than the distance Dx 710 and distance Dy 712.

FIG. 8 illustrates a schematic diagram of an embodiment of a 2Dmonolithic VCSEL array 800 with twenty-five separate laser emitters 802of the present teaching. Each laser emitter 802 has an emission aperture804 of diameter, a. Each laser emitter 802 is formed from multiplesub-apertures 803 that are connected electrically to act as one, andwhose combined emission is contained within an emission aperture 804 ofdimension, a. Thus, each laser emitter 802 generates a laser beam withdiameter, a, equal to the diameter of the emission aperture 804. Thelaser emitters 802 are spaced uniformly in the horizontal direction witha spacing 806, dx. The laser emitters 802 are spaced uniformly in thevertical direction with a spacing 808, dy. The overall size of the arraymeasured from the centers of the outermost lasers is distance 810, Dx,in the horizontal direction and distance 812, Dy, in the verticaldirection. The actual chip size will be slightly larger than thedistance 810, Dx, and distance 812, Dy. FIG. 8 illustrates laseremitters with emission shapes that are circular. In various embodiments,the emitters may produce beams with various shapes. For example, oval,square, rectangular and various odd shapes may be realized. Thisemission width is the width of the shape in a particular direction andwill determine the angular divergence of the LIDAR transmitter in thatparticular direction, as described further below.

Some embodiments of the present teaching utilize bottom-emittinghigh-power arrays of VCSELs with a single large aperture per laser, suchas the configuration shown in FIG. 7. Other embodiments of the presentteaching utilize top-emitting high-power arrays of VCSELs with a largeaperture comprising sub-apertures as shown in FIG. 8. However, oneskilled in the art will appreciate that the present teaching is notlimited to these configurations of top- and bottom-emitting VCSELs andassociated emission apertures.

Prior art systems generate a one-to-one mapping between each laser and aspecific measurement point, and/or projected angle, using a singleshared lens for all the transmitting elements. See, for example, U.S.Pat. No. 7,544,945 that describes utilizing five lasers together with asingle projection lens to form five separate projected beams withdistinct angular spacing. The single projection lens provides twofunctions. The first function is to collimate the laser beam todetermine the spot size of the beam in the far field. The spot size isset by the requirements of the LIDAR system at the required range. Forexample, a typical requirement for LIDAR system is that the laser spotat 100 m should be smaller than 0.5 m in diameter. This is equivalent toa full angle divergence of 5 mrad. The second function of the opticallens is to determine the full field-of-view for the projected laserbeams which is set by the position of the two outermost beams in the farfield at the range of the LIDAR system. The angular resolution betweeneach measurement beam is then determined by the taking the fullfield-of-view divided by the N−1 the number of lasers in each direction.

One disadvantage of prior art single projection lens LIDAR systems isthat they fail to account for the finite size of the emission apertureof the laser emitter. In systems that utilize a single projection lens,the lasers are placed at the focal point of the single projection lensin order to collimate the laser beams.

FIG. 9 illustrates a schematic diagram of light projected by a singlelens LIDAR transmitter system 900. A lens 902 is placed at the focallength 904, f, relative to a plane 906 of a laser emitter. The distance908, y1, represents the half of the emission width, the radius of theemitted laser beam. The angle 910, θ1 is the divergence of the emittedlaser beam. From classical optics, the optical invariant rule tells usthat the product of the beam radius and the beam divergence will be aconstant. Therefore, the laser beam radius 912 after the lens is now y2,and the divergence 914 is θ2, where: θ1*y1=θ2*y2. And from geometry, wesee that the focal length 904, f, is related to y2, by the equation:y2=f*θ1. Combining these two equations, we can then obtain therelationship θ2=y1/f. This relationship indicates that the angulardivergence of the collimated beam is directly related to the focallength of the lens in a single lens LIDAR transmitter. The relationshipalso shows how the angular divergence depends on the width of theemitter size and associated radius for a circular shaped aperture. Thisrelationship sets a minimum size constraint on the lens focal lengthrequired for a particular size of the emitting laser beam. For example,a typical high-power VCSEL has a round shape with an effective emissiondiameter of 100 microns. Therefore, y1 equals 50 microns. To meet thecriteria described herein for a 100 m LIDAR system, there should be lessthan 5-mrad divergence (full angle). The minimum focal length of theprojection lens system is then 20 mm.

The examples described here generally assume a circularly symmetricsystem with a round emission shape and spherical lenses. However, itwill be clear to those skilled in the art that the present teachingsapply to emission shapes and lens shapes having other shapes andgeometries. The width and focal length relationships described thenapply in a particular direction. For example, rectangular emittersand/or lens systems that comprise cylindrical and/or spherical lensescan be used. The choices will depend on the desired beam patterns at thetarget range. For example, a system may be constructed with a differentfield-of-view and angular resolution in the horizontal and verticaldirections.

In the above analysis, we have used classical optics formulations thatassume small angles and thin lenses. If dimensions or angles are large,which is common in compact transmitter designs, the classical opticsformulations would not necessarily provide sufficient accuracy of thepredicted angular divergence and field-of-views obtained. In thesecases, full three-dimensional electromagnetic models are preferred.

FIG. 10 illustrates a schematic diagram 1000 of light projected bymultiple emitters in a single lens LIDAR transmitter system. A singleprojection lens 1002 is situated a distance from an array of VCSEL laseremitters 1004 on a substrate 1006. FIG. 10 illustrates the lightprojected by an arrayed laser transmitter system fully representing theVCSEL laser emitters 1004 as being finite sources with emissionapertures of width, a. In FIG. 10, the center-to-center distance 1008,D, of the outermost lasers, maps to an angular field-of-view 1010, β,which is the center-to-center angular offset between the two outermostprojected beams 1012, 1014. Each vertical position in the focal plane ofthe lens, where the lasers are located, maps to a unique angularprojection angle. As such, for a source of finite emission aperture ofdimension, a, a beam divergence will result approximately equal toa*(β/D).

Referring to FIG. 10, a typical spacing, d, for a VCSEL array would be250 microns, so the center-to-center distance 1008, D, of the outermostemitters would be 1.25 mm. Assuming an emission aperture diameter, a, of100 microns and a maximum divergence full angle of 5 mrad, we cancalculate that the full field-of-view 1010 of the lens, β, cannot begreater than 62.5 mrad (3.58 degrees). If a field-of-view larger than3.58 degrees is generated by the lens, then the divergence of the laserbeam due to the finite size of the laser emission area will exceed 5mrad full angle.

The inherent divergence of the VCSEL laser emitters of FIG. 10 isapproximately two degrees. This low divergence keeps the laser beamslargely separated as they emerge from the plane of the array substrate1006 and proceed through the lens toward the far field, except at thepoint 1016 on the right side of the lens where they all cross over toform a beam waist.

FIGS. 11A-B show a more typical, larger, beam divergence configuration.FIG. 11A illustrates a schematic diagram 1100 of an expanded view oflight projected by multiple emitters in a single lens LIDAR system withhigh angular divergence emitters. FIG. 11B illustrates a schematicdiagram 1150 of a condensed-view of light projected by the system ofFIG. 11A to illustrate the far field. In both figures, an emitter array1102, 1152 illuminates a respective lens 1104, 1154. Each emitter 1106,1156 produces a laser beam 1108, 1158 with a relatively broad divergenceas compared to the example shown in FIG. 10. The lenses 1104, 1154converge the respective emitted beams 1108, 1158 to produce a beam waist1110, 1162. FIGS. 11A-B show how the laser beams would look for a moretypical VCSEL divergence of ˜20 degrees. In this configuration, thebeams 1108, 1158 overlap significantly at the lens 1104, 1154 as shown.And, the position 1160 at which the beams fully separate is much furtherfrom the lens 1154 as compared to the example of FIG. 10, as is shown inFIG. 11B. We can see that the inherent divergence of the VCSEL, alongwith the size of the array, will determine the minimum lens aperture forthis single lens system. The larger the divergence, and the larger thesize of the array, the larger the minimum aperture required to truncatethe laser beams emitted by the VCSEL array.

Thus, for the LIDAR transmitter, we then have two main causes ofdivergence in the transmit beam at the target range in the far fieldthat comprises the series of laser beams emitted by the apertures and/orsub-apertures of the VCSEL array. One source of final beam divergence isa function of the size of the laser emission area and the focal lengthof the lens system. The second source of final beam divergence is afunction of the laser emission size and the projected field-of-view ofthe lens. One feature of the present teaching is the recognition thatdifferent lens systems can be designed with identical focal lengths butwith different projected field-of-views.

A method of light detection and ranging according to the presentteaching includes generating a plurality of optical beams that can bemultiwavelength optical beams. A first lens is positioned in an opticalpath of the plurality of optical beams at a distance from at least oneof the plurality of light emitters that is less than a focal length ofthe first lens. The first lens converges the plurality of optical beamsto a converged optical beam having a beam waist. A second lens ispositioned in the optical path of the converged optical beam so that itprojects the converged optical beam to a target range. The position ofthe second lens can be further selected to decrease an angularresolution of the LIDAR transmitter at the target range. Also in somemethods, a size of an aperture of the second lens is chosen to be equalto a size of the beam waist of the converged optical beam. The positionof the second lens and an emission width of at least one of theplurality of light emitters are selected to provide a desiredfield-of-view of the LIDAR transmitter at the target range.

FIG. 12 illustrates a schematic diagram of an embodiment of a lenssystem that projects light in a small angular divergence LIDARtransmitter 1200 of the present teaching. A first lens 1202 is placed invery close proximity to the VCSEL laser array 1204 that comprisesmultiple individual laser emitters 1206. The first lens 1202 may beplaced closer to the emitters than a distance equal to the focal lengthof the first lens. The figure illustrates laser beams 1202, 1210 thatare emitted by the individual laser emitters 1206. Only the center laserbeam 1208 and an outer laser beam 1210 are shown. But all the laseremitters 1206 in the array may produce laser beams, as desired.

A second lens 1212 is positioned after the first lens 1202 and projectsthe laser beams 1208, 1210 to a far field position 1214 where the laserbeams from individual transmitters are nominally separated. The firstlens 1202 is placed at a particular distance 1216 from the array thatproduces a desired convergence of the laser beams 1208, 1210 at thesecond lens 1212. The second lens 1212 is placed at a particulardistance 1218 from the first lens 1202 to produce a desiredfield-of-view at a desired far field position 1214, the target range.

As shown in FIG. 12, the first lens 1202 acts to converge the beams,turning the laser beam 1210 inward from the outermost VCSEL emitter1220, which produces a smaller minimum lens aperture for the second lens1212 as compared to a single lens system. This means the physicaltransmitter can be smaller in size because the minimum lens aperture ofthe second lens 1212 determines the size of the largest lens in thesystem. In this example, the beam waist produced by the converging firstlens 1202 is formed at the position of the second lens 1212, and theaperture of the second lens is equal to the size of the beam waist. Eachof the beams produced by the emitters fills the aperture of the secondlens.

This two-lens configuration, when compared to a single lens system, withidentical focal lengths, has significantly improved performance whilemaintaining the required low divergence of the output beams. Thistwo-lens configuration also advantageously minimizes the size of theLIDAR transmitter. In addition, the projection angle of the two-lenssystem can be varied without changing the overall focal length of thelens system. The curvatures of the lens surfaces in this two-lens systemcan be adjusted to provide an additional degree of freedom thatmaintains focal length, while enabling different field-of-view. Thisadditional degree of freedom also allows the adjustment of thefield-of-view to minimize as necessary the divergence of the individualemitted laser beams, while maintaining an overall compact size for thetransmitter.

As described herein, the divergence of the transmitted laser beams ofthe individual laser emitters is a critical factor in determining theresulting field-of-view of the lens system. Once the maximumfield-of-view is determined based on the maximum divergence, the angularresolution of the system is then determined by the spacing betweenindividual lasers in the array, which cannot be smaller than theindividual emission width.

The small angular divergence LIDAR transmitter of the present teachingcan be configured in a variety of designs that realize particularfield-of-views and angular resolutions that are required to address theneeds of the particular sensor application. For example, some automotiveapplications require a maximum divergence that is five milliradians halfangle. Field-of-view, divergence and aperture size are all related.Furthermore, the emitter emission width, emitter pitch, and array sizeare critical. In one particular embodiment, a sixteen-by-sixteen-elementtwo-dimensional array with an emission width of 125 micron and laserpitch of 250 micron, and a maximum half-angle divergence of 5 mrad isconfigured for a field-of-view of 18.3 degrees by using a two lenssystem in which the first lens is placed at a position less than thefocal length of the first lens from the array. A larger field-of-viewusing the present teachings is possible, for example using a smalleremission width.

The angular resolution is determined by dividing the field-of-view bythe array size. Using the smallest possible emission-width emittersmeans more elements in the array, and hence the smallest possibleangular resolution. One particular embodiment with a sixteen-elementarray in one dimension, an emission width of 50 micron, a laser pitch of250 micron, and a maximum half-angle divergence of 5 mrad is configuredfor a field-of-view of 45.8 degrees. The angular resolution for thisconfiguration is 2.8 degrees. A smaller resolution is possible, forexample, using more array elements with a smaller pitch.

In various embodiments, the field-of-view and the angular resolution maybe different in different directions, for example, in some systems, thehorizontal field-of-view and angular resolution are different from thevertical field-of-view and angular resolution.

One feature of the present teaching is that the compact size of thetwo-lens projection system, and other design features, allow formultiple transmitter arrays to be combined into a single transmittersystem. FIG. 13 illustrates a schematic diagram of an embodiment of alens system that projects light in a small angular divergence LIDARtransmitter 1300 utilizing multiple transmitter arrays 1302, 1304, 1306according to the present teaching. In FIG. 13, several transmitterarrays 1302, 1304, 1306 are used to cover a combined wider field-of-view1308. The individual VCSEL emitters each use a transmitter arrays 1302,1304, 1306, and the placement of the transmitter arrays 1302, 1304, 1306in three dimensional space (x, y, z) allows the beams to be combined ina desired pattern, such as an overall uniform pattern in the far fieldor a pattern with desired overlap or gaps.

For example, the positions of the transmitter arrays 1302, 1304, 1306may be chosen so that the pattern of beams at the target range arearranged so the beams from the first transmitter array 1302 and thebeams from the second transmitter array 1304 form a gap at the targetplane. Alternatively, the positions of the transmitter arrays 1302,1304, 1306 may be chosen so that the pattern of beams at the targetrange are arranged so the beams from the first transmitter array 1302and the beams from the second transmitter array 1304 overlap at thetarget plane. In addition, the positions of the transmitter arrays 1302,1304, 1306 may be chosen so that the pattern of beams at the targetrange are arranged so the beams from the first transmitter array 1302and the beams from the second transmitter array 1304 form a uniformpattern of light at the target plane. It will be clear to those withskill in the art that the relative positions of the transmitter arrays,and associated optical lenses that converge and project the multiplebeams that emerge from the transmitter arrays allow a variety ofpatterns to be projected at the target plane.

In some embodiments, the multiple transmitter arrays are used to cover awider, or narrower, field-of-view by physically adjusting the position(x, y, z) and pointing angle of the individual transmitters, using allsix dimensions to produce a desired pattern of laser beams at the targetrange. The various patterns of laser beams at the target range produceassociated desired measurement point clouds when utilized in a LIDARsystem.

In one embodiment, at least two transmitter arrays are positioned sothat the beams substantially overlap at the target range. In thisembodiment, the field-of-view of a two-transmitter system is the same asthe field-of-view of each transmitter array and lens system. Systemswith more than two arrays can also be configured with substantiallycompletely overlapping patterns at the target range. Such an arrangementleads to improved angular resolutions. Embodiments of the presentteaching using multiple emitter arrays are capable of achieving angularresolution of less than 0.25 degrees using state-of-the-art emitterarray technology.

One feature of the present teaching is that multiple transmitter arrayscan be placed on a single substrate. Each transmitter array can have adifferent shape and spacing, and the spacing between each transmitterarray can also be varied on the substrate. FIG. 14A illustrates aschematic diagram of an expanded view an embodiment of a lens systemthat projects light in a small angular divergence LIDAR transmitterutilizing multiple transmitter arrays on a single substrate of thepresent teaching.

FIG. 14B illustrates a schematic diagram of a condensed-view of theembodiment of a lens system that projects light in a small angulardivergence LIDAR transmitter of FIG. 14A. Multiple transmitter arrays1402, 1404, 1406, 1408 are positioned on a common substrate 1410. Eachtransmitter array 1402, 1404, 1406, 1408 has an associated first lens1412, 1414, 1416, 1418, and second lens 1422, 1424, 1426, 1428. Forclarity, FIGS. 14A-B do not show the full diverging laser beams emittedby each VCSEL emitter, instead a single ray from the center of threeVCSEL emitters are shown to illustrate the concept of the presentteaching. For each transmitter array 1402, 1404, 1406, 1408, a singleray from a top outer emitter 1432, 1434, 1436, 1438 is shown. Also, foreach transmitter array 1402, 1404, 1406, 1408, a single ray from abottom outer emitter 1442, 1444, 1446, 1448 is shown. For eachtransmitter array 1402, 1404, 1406, 1408, a single ray from a centralouter emitter 1452, 1454, 1456, 1458 is shown. The embodiment of FIG.14A-B uses multiple array transmitters 1402, 1404, 1406 to increase theangular resolution. For a single transmitter array that uses a singleVCSEL array on a substrate, the angular resolution is set by thefield-of-view and the number of individual lasers emitters in the array.If denser angular resolution is desired, then multiple transmitters canbe combined by overlapping the output beams in the far field at thedesired range.

FIG. 14A illustrates the four transmitter arrays 1402, 1404, 1406, 1408are attached to a common substrate 1410. While a common substrate is notnecessary, it may be desired from an ease-of-assembly point-of-view. Avariety of known common substrates may be used including those formed ofa semiconductor material or a ceramic material. The common substrate maybe a printed circuit board (PCB). In some embodiments, some of thetransmitter arrays share one common substrate, for example a singlesemiconductor or ceramic carrier substrate. In other embodiments, thetransmitter arrays are on a different common substrate, and then thesetwo common substrates with arrays are placed on a third commonsubstrate, for example a PC board.

Each of the four transmitter arrays 1402, 1404, 1406, 1408 has its owncorresponding lens system comprising a first lens 1412, 1414, 1416, 1418and a second lens 1422, 1424, 1426, 1428 corresponding to eachtransmitter array 1402, 1404, 1406, 1408, as shown. The laser beamsemanating from the four transmitter arrays 1402, 1404, 1406, 1408 areoverlapped and combined by adjusting the position of each of the fourlens systems, comprising a first lens 1412, 1414, 1416, 1418 and asecond lens 1422, 1424, 1426, 1428, relative to the position of theircorresponding transmitter array 1402, 1404, 1406, 1408. The position ofthe second lens 1422, 1424, 1426, 1428 in each transmitter is shown atdifferent radial offsets 1452, 1454, 1456, 1458 of P1, P2, P3, and P4from the center of each corresponding transmitter array 1402, 1404,1406, 1408. The first lens 1412, 1414, 1416, 1418 for each transmitterarray 1402, 1404, 1406, 1408, can also be radially offset from thecenter of its associated transmitter array 1402, 1404, 1406, 1408. Theseoffsets will allow each transmitter array 1402, 1404, 1406, 1408 toachieve a desired beam pattern at the target range. The exact radialoffset values are chosen as needed to create a specific angular fieldpattern required by the LIDAR system at range. These radial offsetvalues are not typically equal, but can be equal in particularembodiments.

One feature of the present teaching is that the lateral offset betweenthe separate VCSEL arrays is not critical to determining the combinedbeam pattern at the target range. FIG. 14A illustrates lateral offsets1460, 1462, 1464 with values of S1, S2, and S3. The exact values of S1,S2, and S3 for a LIDAR system with typical range of 100 m are notcritical as the offset is not magnified with distance. In manyembodiments, after only a few meters, the initial offset between arrays,represented by lateral offsets 1460, 1462, 1464 in the figure, is nolonger significant compared to the offset due to the difference inprojection angles that are set by the lens system for each array. Thecondensed-view of FIG. 14B shows a representation of how the beamscombine in the far field.

The relative independence of the projected field pattern for lenssystems of the present teaching on the lateral offset of the arrays isillustrated by the configuration shown in FIG. 15. FIG. 15 illustratesschematic diagrams of scaled condensed and expanded views of embodimentsof the small angular divergence LIDAR transmitters of the presentteaching to show relative independence of the separation betweentransmitter arrays. FIG. 15 illustrates scale examples of laser beamsbeing combined. An expanded-view and a condensed-view are shown. In oneconfiguration, the initial lateral offset is equal to 10 mm in theexpanded-view 1502 and in the condensed-view 1504. In anotherconfiguration 1506, the initial lateral offset is equal to 20 mm in theexpanded view 1506 and in the condensed-view 1508.

In one particular embodiment, the laser beams for each VCSEL array areoffset 2-degree, and there is a 1-degree offset between the transmitterssuch that the laser beams in the final beam pattern are uniformly offsetby 1 degree in the far field. It can be seen at ˜5 m that there is nosubstantial difference in the far field patterns.

One feature of the present teaching is that the lens systems are capableof controlling both the divergence and the step size or position of thebeams in the far field. Known LIDAR projection systems typically controlstep size only, and do not have the ability to control both thedivergence and the step size or position of the beams in the far fieldindependently. Furthermore, LIDAR systems of the present teaching canintroduce additional beam control of the far field pattern by usingadditional optical elements. In particular, by positioning the firstlens in close proximity to the transmitter array, the lens system of thepresent teaching provides a different step size independent of the focalof the optical system.

One feature of the LIDAR systems of the present teaching is the abilityto use wavelength to provide control over the laser beam patterngenerated in the far field at the target range, and associatedmeasurement point cloud of the LIDAR system. FIG. 16 illustrates anembodiment of an illuminator 1600 for a multi-wavelength LIDAR systemusing multiple transmitter arrays of the present teaching. In thisembodiment, a plurality of surface emitting laser arrays comprising atleast two groups of lasers with different wavelengths, VCSEL λ1 1602,and VCSEL λ2 1604 are used.

Another feature of the LIDAR systems of the present teaching is use ofthree-dimensional space. VCSEL λ1 1602 and VCSEL λ2 1604 are oriented intwo surfaces that are orthogonal to each other. One skilled in the artwill appreciate that a variety of three-dimensional (X, Y, and Z)degrees of freedom, and/or six-dimensional degrees of freedom (X, Y, Z,pitch, yaw, and roll) that include the angles of the VCSELs 1602, 1604can be used in the LIDAR system of the present teaching. The beams arecombined by use of a wavelength multiplexer 1806 that passes onewavelength, while reflecting the second wavelength.

The wavelength multiplexer 1606 can be realized, for example, by use ofa thin film filter that allows the first wavelength to pass throughundeflected, while the second wavelength is deflected at 45 degrees, andthe output beams are combined. For simplicity, we have shown themultiplexer 1606 in the shape of cube formed by two equal prisms oftriangular cross-section, where the thin film filter that reflects orpasses the wavelengths is located at the central plane of the cube wherethe two triangular prisms touch.

The positions of the two substrates of VCSEL λ1 1602 and VCSEL λ2 1604can be shifted laterally, relative to the wavelength multiplexer 1606,to create the desired overlap or interleaving of the two beams. FIG. 17illustrates a measurement point cloud 1700 that can be generated withthe illuminator embodiment of FIG. 16. It will be clear to those skilledin the art that the use of laser emitters with different wavelengths isnot limited to the configurations illustrated here. Differentwavelengths may be associated with each array, or different wavelengthsmay be emitted from a single array in various patterns. In addition, thearrays may be configured in a variety of 3D spatial patterns includingdifferent emission angles for each array.

One feature of the present teaching is that the optical projectionsystem accounts for the finite emission area of the VCSEL lasers thatform the emitter array. Known LIDAR projection optics model the lasersource as a point source. In some embodiments of the LIDAR system of thepresent teaching, each of the adjacent VCSELs within the array have aseparation pitch greater than the individual diameter of the emissionarea of each laser. The array of VCSEL lasers all share a common opticallens system with a clear aperture that is smaller than the projectedcombined diameter of the array of VCSEL lasers in free space. This isaccomplished by a first lens that converges at least the outermostbeams. In some embodiments, the first lens, which is the converginglens, is positioned adjacent to the VCSEL array at a distance that isshorter than the focal length of the first lens. The maximum angularfield-of-view of the lens system is defined by the emission width of thelaser, the optical system defining a divergence of the laser beam, andthe separation pitch of the lasers in the array.

In some embodiments, multiple transmitter arrays are overlapped in freespace to create a denser angular resolution than can be created with asingle transmitter with the same VCSEL array dimensions. Eachtransmitter array has an associated first lens. The first lenses of eachindividual transmitter array are radially offset to produce a differentangular pattern. The radial offsets of each lens system do not need tobe the same. The transmitter arrays are located on a common substrateand the distances between the various transmitter arrays do not need tobe the same. In embodiments with multiple transmitters, the wavelengthsof the individual VCSELS that comprise the transmitter array and/or eachtransmitter array may be the same or different. In embodiments of theLIDAR system of the present teaching that use different wavelengths, awavelength sensitive element may be used to further converge or divergethe beams in the far field based on their wavelength.

A method of light detection and ranging according to the presentteaching includes providing a first transmitter array comprising a firstplurality of light emitters that generate a first plurality of opticalbeams that can be multiwavelength optical beams. A first lens ispositioned in an optical path of the first plurality of optical beams ata distance from at least one of the plurality of light emitters that isless than a focal length of the first lens so that the first lensconverges the first plurality of optical beams to form a first convergedoptical beam with a beam waist. A second lens is positioned in theoptical path of the first converged optical beam so that it projects thefirst converged optical beam to a target range. The position of thesecond lens and an emission width of at least one of the first pluralityof light emitters are selected to provide a desired field-of-view of theprojected first converged optical beam at the target range.

The method also includes providing a second transmitter array comprisinga second plurality of light emitters that generate a second plurality ofoptical beams that can be multiwavelength optical beams. A third lens ispositioned in an optical path of the second plurality of optical beamsat a distance from at least one of the second plurality of lightemitters that is less than a focal length of the third lens so that thethird lens converges the second plurality of optical beams to form asecond converged optical beam with a beam waist. A fourth lens ispositioned in the optical path of the second converged optical beam sothat the fourth lens projects the second converged optical beam to atarget range. The position of the fourth lens and an emission width ofat least one of the second plurality of light emitters are selected toprovide a desired field-of-view of the projected second convergedoptical beam at the target range. A position of the first transmitterarray and a position of the second transmitter array are chosen toprovide a desired field-of-view of the LIDAR transmitter at the targetrange.

EQUIVALENTS

While the Applicant's teaching is described in conjunction with variousembodiments, it is not intended that the Applicant's teaching be limitedto such embodiments. On the contrary, the Applicant's teachingencompasses various alternatives, modifications, and equivalents, aswill be appreciated by those of skill in the art, which may be madetherein without departing from the spirit and scope of the teaching.

What is claimed is:
 1. A light detection and ranging (LIDAR) transmittercomprising: a) a plurality of light emitters that generate a pluralityof optical beams; b) a first lens positioned in an optical path of theplurality of optical beams at a distance from at least one of theplurality of light emitters that is less than a focal length of thefirst lens, the first lens converging the plurality of optical beams toa converged optical beam having a beam waist; and c) a second lenspositioned in the optical path of the converged optical beam, the secondlens projecting the converged optical beam to a target range, whereinthe position of the second lens and an emission width of at least one ofthe plurality of light emitters are configured to provide a desiredfield-of-view of the LIDAR transmitter at the target range.
 2. The LIDARtransmitter of claim 1 wherein the position of the second lens isfurther chosen to decrease an angular resolution of the LIDARtransmitter at the target range.
 3. The LIDAR transmitter of claim 1wherein a size of an aperture of the second lens is equal to a size ofthe beam waist of the converged optical beam.
 4. The LIDAR transmitterof claim 1 wherein the plurality of light emitters form an array oflight emitters.
 5. The LIDAR transmitter of claim 4 wherein a size ofthe beam waist of the converged optical beam in a direction is less thanor equal to a size of the array in the direction.
 6. The LIDARtransmitter of claim 4 wherein an optical beam generated by a centerlight emitter of the array of light emitters and an optical beamgenerated by an outermost light emitter of the array of light emittersfill an aperture of the second lens.
 7. The LIDAR transmitter of claim 1wherein at least two of the plurality of light emitters emit light withdifferent wavelengths.
 8. The LIDAR transmitter of claim 1 wherein theplurality of light emitters comprises a plurality of VCSEL devices. 9.The LIDAR transmitter of claim 8 wherein the plurality of VCSEL devicescomprise a two-dimensional VCSEL array.
 10. The LIDAR transmitter ofclaim 8 wherein the VCSEL devices are configured as top-emitting VCSELdevices.
 11. The LIDAR transmitter of claim 8 wherein the VCSEL devicesare configured as bottom-emitting VCSEL devices.
 12. The LIDARtransmitter of claim 8 wherein the plurality of light emitters comprisesa monolithic VCSEL array with each of the plurality of VCSEL devicesformed on a common substrate.
 13. The LIDAR transmitter of claim 1wherein the position of the second lens and the emission width of atleast one of the plurality of light emitters are configured to provide adesired field-of-view of the LIDAR transmitter at the target range thatis greater than eighteen degrees.
 14. The LIDAR transmitter of claim 1wherein the position of the second lens is further chosen to so that anangular resolution of the LIDAR transmitter at the target range is lessthan 2.8 degrees.
 15. A light detection and ranging (LIDAR) transmittercomprising: a) a first transmitter array comprising a first plurality oflight emitters that generate a first plurality of optical beams; b) afirst lens positioned in an optical path of the first plurality ofoptical beams at a distance from at least one of the plurality of lightemitters that is less than a focal length of the first lens, the firstlens converging the first plurality of optical beams to form a firstconverged optical beam with a beam waist; c) a second lens having aposition in the optical path of the first converged optical beam, thesecond lens projecting the first converged optical beam to a targetrange, wherein the position of the second lens and an emission width ofat least one of the first plurality of light emitters are configured toprovide a desired field-of-view of the projected first converged opticalbeam at the target range; d) a second transmitter array comprising asecond plurality of light emitters that generate a second plurality ofoptical beams; e) a third lens positioned in an optical path of thesecond plurality of optical beams at a distance from at least one of thesecond plurality of light emitters that is less than a focal length ofthe third lens, the third lens converging the second plurality ofoptical beams to form a second converged optical beam with a beam waist;and f) a fourth lens having a position in the optical path of the secondconverged optical beam, the fourth lens projecting the second convergedoptical beam to a target range, wherein the position of the fourth lensand an emission width of at least one of the second plurality of lightemitters are configured to provide a desired field-of-view of theprojected second converged optical beam at the target range, wherein aposition of the first transmitter array and a position of the secondtransmitter array are chosen to provide a desired field-of-view of theLIDAR transmitter at the target range.
 16. The LIDAR transmitter ofclaim 15 wherein the position of the first transmitter array and theposition of the second transmitter array are chosen to provide a uniformoptical beam pattern at the target range.
 17. The LIDAR transmitter ofclaim 15 wherein the position of the first transmitter array and theposition of the second transmitter array are chosen to provide a patterncomprising a gap between the projected first converged optical beam andthe projected second converged optical beam at the target range.
 18. TheLIDAR transmitter of claim 15 wherein the position of the firsttransmitter array and the position of the second transmitter array arechosen to provide a pattern comprising an overlap between the projectedfirst converged optical beam and the projected second converged opticalbeam at the target range.
 19. The LIDAR transmitter of claim 15 whereina position of a center of the first lens in the optical path of thefirst plurality of optical beams is at a first distance from a center ofthe first transmitter array and a position of a center of the third lensin the optical path of the second plurality of optical beams is at asecond distance from a center of the second transmitter array and thefirst and second distance are different.
 20. The LIDAR transmitter ofclaim 15 wherein the first and second transmitter arrays are positionedon a common substrate.
 21. The LIDAR transmitter of claim 15 furthercomprising a third transmitter array comprising a third plurality oflight emitters that generate a third plurality of optical beams, whereina distance between the first transmitter array and the secondtransmitter array is different from a distance between the secondtransmitter array and the third transmitter array.
 22. The LIDARtransmitter of claim 21 wherein the first, second and third transmitterarrays are positioned on a common substrate with non-uniform spacing.23. The LIDAR transmitter of claim 15 wherein at least two of the firstplurality of light emitters emit light with different wavelengths. 24.The LIDAR transmitter of claim 23 wherein at least two of the secondplurality of light emitters emit light with different wavelengths. 25.The LIDAR transmitter of claim 15 wherein at least one of the firstplurality of emitters and at least one of the second plurality ofemitters emit light with different wavelengths.
 26. The LIDARtransmitter of claim 15 wherein at least one of the first and secondtransmitter arrays comprises a two-dimensional array.
 27. The LIDARtransmitter of claim 15 wherein at least one of the first or secondplurality of light emitters comprises a plurality of VCSEL devices. 28.The LIDAR transmitter of claim 27 wherein the plurality of VCSEL devicescomprise a two dimensional VCSEL array.
 29. The LIDAR transmitter ofclaim 27 wherein the VCSEL devices are top-emitting VCSEL devices. 30.The LIDAR transmitter of claim 27 wherein the VCSEL devices arebottom-emitting VCSEL devices.
 31. The LIDAR transmitter of claim 15wherein the position of the second lens and the emission width of atleast one of the first plurality of light emitters are configured toprovide the desired field-of-view of the projected first convergedoptical beam at the target range that is greater than eighteen degrees.32. The LIDAR transmitter of claim 15 wherein the first and secondtransmitter array are configured so that an angular resolution of theLIDAR transmitter at the target range is less than 0.25 degrees.